PHOTOREFRACTIVE NONLINEARITY OF PERIODICALLY POLED FERROELECTRICS

We study theoretically the dependence of the photorefractive response of a periodically poled ferroelectric on the spatial frequency of ligh t fringes, on the period of the domain inversion, and on its mark-to-s pace ratio. The photovoltaic effect, the drift of photoelectrons under an applied field, and their diffusion are considered as charge-transp ort mechanisms. Strong suppression of the photorefractive properties a t low spatial frequencies (reduction of optical damage) together with retention of these properties in a region of short-fringe spacing are shown. We also found that the periodicity of the domain structure can produce a new kind of photorefractive parametric wave coupling. This c oupling is characterized by a large gain factor for the waves propagat ing at angles that depend on the domain-inversion period. Finally, we discuss promising photorefractive experiments in periodically poled li thium niobate. (C) 1997 Optical Society of America.